Question

7 planks are made using a few twigs. 3 twigs are left at the end. If 1 plank is made of 10 twigs, select the correct representation that shows the total number of twigs that were there in the beginning.

• A.
• B.
• C.
• D.

Answer 1

The correct option is D

Say: Let’s find out the number of twigs that were at the beginning as per the given data.

Steps:
$\bullet$ 7 planks are made. Each plank uses 10 twigs, which is 1 Ten.
$\bullet$ Therefore, the number of twigs used for making 7 planks = 7 Tens or 70.
$\bullet$ There are 3 twigs left, which is 3 Ones.
$\bullet$ To represent this on the abacus, there must be 7 beads over “T” representing 7 Tens and 3 beads over “O” representing 3 Ones.
$\bullet$ 7 Tens and 3 Ones = 73.
$\bullet$ Option C has the correct beads.
$\bullet$ Hence, Option C is correct.

twigs are used to make 1 plank.

Q: How will the new number of twigs be represented on abacus?
A: The new number of twigs will be 80. It will be represented on the abacus by placing 8 beads over “T” and no beads over “O”.